Peritoneal mesothelium exposed to asbestos by either intraperitoneal and/or intra-abdominal wall administration will be studied in mice serially sacrificed. Investigation will include gross anatomy, histology, histochemistry and electron microscopy. Questions to be investigated include: 1) Are there favorite sites for the primary focus in the induced mesothelioma after the administration? 2) The evolution of the mesothelium from normal to neoplastic. 3) Are asbestos fibrils commonly and preferentially seen around the neoplastic mesothelium at early stages? 4) Identification of floating mesothelioma cells in peritoneal effusions. 5) Response of mesothelioma upon transplantation into nude mice as well as in the same strain of mice. 6) The comparative pathology of animal and human mesothelioma.